title: Maitotoxin-induced myocardial cell injury: calcium accumulation followed by ATP depletion precedes cell death.
abstract: Maitotoxin, the most potent marine toxin, is known to increase the uptake and the accumulation of Ca2+ into cells, and was used in the present study to investigate the mechanisms of myocardial cell damage induced by Ca2+ overload. In cultured cardiomyocytes, isolated from 2-day-old rats, maitotoxin affected cell viability, as indicated by the leakage of the cytosolic enzyme lactate dehydrogenase (LDH) and of radiolabeled adenine nucleotides into the extracellular medium. Maitotoxin-induced leakage of LDH steadily increased between 30 min and 24 hr, and was preceded by a marked depletion of intracellular ATP. Addition of maitotoxin resulted in a rapid influx of extracellular Ca2+, as detected by preincubating the cells in the presence of 45Ca; this effect evolved in a few minutes, thus preceding the signs of cell death. Cytosolic levels of free Ca2+ ([Ca2+]i) were monitored by loading freshly isolated, suspended cardiomyocytes with the intracellular fluorescent probe fura-2; in these cells, maitotoxin induced a dose-dependent increase in [Ca2+]i, with a lag phase of less than a minute. All these effects of maitotoxin were inhibited by reducing Ca2+ concentration in the culture medium or by incubating the cells with the calcium-channel blocking drug verapamil. It is thus demonstrated that maitotoxin-induced cardiotoxicity is secondary to an inordinate influx of Ca2+ into the cells. It is also suggested that, in those conditions that lead to an inordinate accumulation of Ca2+ into myocardial cells, the unmatched demands of energy and the depletion of ATP play a primary role in the irreversible stage of cell damage.
authors.affiliation: Section on Drug Tissue Interaction, National Heart, Lung and Blood Institute, Bethesda, Maryland.
authors.forename: G
authors.initials: G
authors.lastname: Santostasi
authors.forename: R K
authors.initials: RK
authors.lastname: Kutty
authors.forename: A L
authors.initials: AL
authors.lastname: Bartorelli
authors.forename: T
authors.initials: T
authors.lastname: Yasumoto
authors.forename: G
authors.initials: G
authors.lastname: Krishna
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008387:Marine Toxins / Q000633:toxicity*; D009206:Myocardium / Q000378:metabolism*; D035964:Oxocins; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D000095702:Polyether Toxins
chemical_list: D000255:Adenosine Triphosphate; D002118:Calcium; D002250:Carbon Radioisotopes; D007770:L-Lactate Dehydrogenase; D008387:Marine Toxins; D035964:Oxocins; C020394:maitotoxin; D000095702:Polyether Toxins